This invention relates to tuning apparatus and, more particularly, to tuning apparatus which is tunable to desired ones of broadcast frequencies, such as FM and AM broadcast frequencies.
In many geographic locations, and particularly, larger metropolitan areas, a large number of FM and AM radio stations are provided. Thus, a user who has a home entertainment tuning device may receive a multitude of FM and AM broadcast frequencies. Often, the user may prefer to listen to the program entertainment which is transmitted over a relatively small number of such available broadcast frequencies. If a particular program received over one of these broadcast frequencies is not satisfactory, the user may adjust his tuning device so as to receive the program which is transmitted over another preferred broadcast frequency. However, many receivable broadcast frequencies may exist in the frequency band between the two stations to which the user tunes his tuning device. As the tuning condition of this device is changed, the programs which are transmitted via those intermediary broadcast frequencies will be received. Since the tuning condition of the tuning device is changed abruptly during this station-changing operation, the brief reception of undesired broadcast frequency information may be quite annoying and distracting to the user.
In order to rapidly change the tuning condition of a radio receiver from one station to another without accompanying undesired program information which is present in those broadcast frequencies which lie between the two stations, push-button radio tuning apparatus has been proposed. Such push-button tuning devices are used advantageously in automotive radio receivers. However, such push-button tuning devices generally are not provided in high fidelity home entertainment tuning apparatus.
Recently, frequency synthesizer tuning devices have been proposed. One such frequency synthesizer tuning device is disclosed in U.S. Pat. No. 3,962,641, assigned to the assignee of the present invention. In this frequency synthesizer tuning device, the usual adjustable air capacitor, which heretofore had been used for tuning a device to a desired frequency, is replaced by a phase-locked loop having a voltage controlled oscillator whose frequency is determined by a programmable frequency divider which, in turn, has a frequency dividing ratio which is established by a digital signal representing a particular radio station. When a desired radio station is selected, the digital signal corresponding to that station establishes a corresponding frequency dividing ratio. The frequency of the oscillating signal produced by the voltage controlled oscillator is divided by the established, or programmed, dividing ratio, and the frequency-divided frequency is compared to a reference frequency. Any difference therebetween is used to adjust the frequency of the voltage controlled oscillator such that the frequency-divided version thereof is equal to the reference frequency. In this manner, the frequency of the voltage controlled oscillator, before frequency division, establishes the tuning condition of the tuning device which is necessary to receive the desired station information. It is desirable to provide, in a frequency synthesizer tuning device, presettable means whereby the tuning apparatus can be rapidly and accurately tuned to preset FM and/or AM radio stations. It also is desirable to provide, in such tuning apparatus, the ability to change the preset FM and/or AM stations in accordance with the particular preferences of the user.